Objective: To determine whether an arterial 'steal' from the ophthalmic artery accounts for the ocular manifestations associated with maxillofacial arteriovenous malformation (AVM) outside the orbit. Design: Retrospective noncomparative case series. Participants: Seven patients with maxillofacial AVM who had been previously treated, unsuccessfully, with proximal ligation of the supplying external carotid artery branches were evaluated clinically and by superselective cerebral angiography. No cases had intraorbital arteriovenous shunting or abnormal venous drainage to the orbit. Intervention: Endovascular embolization. Main Outcome Measures: Signs and symptoms of ocular ischemia were correlated with findings on cerebral/orbital angiography. Results: Four of seven patients had signs of ocular ischemia. By selective angiography, these four patients were found to have a significant ophthalmic artery supply to the AVM. In contrast, the three patients without signs of ocular ischemia had minimal or no ophthalmic artery supply to the AVM. Conclusions: When the ophthalmic arterial blood supply is recruited, ophthalmic artery 'steal' phenomenon occurs in patients with maxillofacial AVMs that do not directly involve the orbit. This mechanism appears to be the cause of ocular ischemia. It is possible that this 'steal' is precipitated or worsened by previous surgical proximal ligation of external carotid arterial branches that are potential collaterals with the ophthalmic artery but fail to occlude the arteriovenous (AV) shunts. (C) 2000 by the American Academy of Ophthalmology.